Two Aerobee rockets were employed to eject relatively large amounts of sodium vapor into the earth's atmosphere. One of the flights occurred during evening twilight and sodium was placed in the sunlit atmosphere from 75 to 110 km. Sodium D‐line emission (λ 5890 A) was observed in the ejected trail above 90 km, and 5890 A is discussed in terms of resonance scattering of solar radiation. Below 90 km, D‐line radiation was not apparent, and the trail was white in appearance. This requires the formation of aerosols and indicates that sodium is unlikely to remain in the atomic state below 90 km.The second flight occurred at night. Strong D‐line emission and a persistent trail were observed at about 65 km, 100 km, and 140 km. This emission is discussed in terms of chemical processes which have been proposed to explain the sodium airglow. These processes cannot produce the observed brightness of the trail at the high altitudes. Excited atomic nitrogen (N2D) is proposed as a possible source of the energy. The observed presence of large amounts of energy stored in the earth's atmosphere above 100 km requires revision of some of the proposals regarding the sodium airglow and its